Substantial evidence exists indicating that the ability of certain growth factors and hormones to regulate cell proliferation may depend on a synergistic interaction with extracellular and/or plasma membrane-bound Ca2+and that this relationship may be modified in transformed cells. Transformed cells exhibit reduced growth factor or serum requirements and a reduced requirement for extracellular Ca2+. Ca2+appears to modulate either serum or EGF requirements for fibroblasts and epithelial cells, and recent reports indicate Ca2+requirements for EGF, NGF, and insulin binding and/or internalization and degradation. We have demonstrated a Ca2+requirement in early and late G1 phase for human and mouse fibroblasts, and this has been confirmed by others in rat fibroblasts. The absence of Ca2+at either of these positions in G1 phase prevents GO-early G1 exit and late G1 to S phase entrance. We now will investigate these Ca2+requirements in regard to recent evidence dealing with growth factor-hormone (GFH) regulation of G1 progression and rate of entry to S phase. These two processes are conceivably regulated at the same time specific Ca2+requirements have been identified in the G1 phase. We shall evaluate the changes in Ca2+transport and compartmentation during G1 phase and their sensitivity to various GFH treatments using isotope flux techniques. We shall evaluate the ability of GFH to alter the lag phase versus rate of entry to S phase and establish whether such effects relate to Ca2+metabolism. We shall evaluate the relationship of GFH to the regulation of four membrane transport systems, which we have demonstrated to be regulated by serum and Ca2+. We shall evaluate Ca2+metabolism and its regulation by various GFHs during G1 phase in the transformed fibroblast. This should be possible due to our recent ability to syn-chronize SV40-transformed cells. Essentially no information is available regarding these processes in transformed cells. Lastly, we shall examine effects of serum growth conditions versus defined media growth conditions on Ca2+metabolism, since recent reports indicate that ionic metabolism may well differ under the two growth states. (N)